Zoom-in of RRL spectra towards M 42 around the carbon feature. The RRLs correspond to α lines with principal quantum numbers 137, 145, 155, 156, 164, 174, 199, 280, and 351. CRRLs withn ≤ 199 appear in emission, while those with n ≥ 280 appear in absorption. The velocity is given with respect to the CRRL and the intensity axis is normalized to the peak of the CRRL. To reference the velocity with respect to helium, 27.4 km s⁻¹ was subtracted. The spectra are offset by a constant 0.6 and are normalized using the peak of the brightest CRRL in each spectra. The dotted lines indicate the position of the CRRLs at ≈1.3, ≈ 6, and ≈ 8 km s⁻¹ (black) and the HeRRL (blue). The C351α spectrum is the spatial average over a circle 36′ in diameter centered on M 42.